Figure 2
From: A low cost, short range quantum key distribution system
The scheme of combining multiple sources into one spatial mode. The LEDs (a) are individually polarized by a patterned polarizer (b). The LEDs are placed closely so their emission cones overlap and an optical fibre is placed such that its NA overlaps the LEDs (c). The fibre is bent to remove cladding modes (d) and the fibre output is single moded (e)